167 



III. " Observations on the Respiratory Movements of Insects." 

 By the late WILLIAM FREDERICK BARLOW, F.R.C.S. 

 Arranged and communicated by JAMES PAGET, F.R.S. 

 Received August 20, 1854. 



This essay contains the greater part of a series of observations 

 made between 1845 and 1850. The following are some of the 

 conclusions which they plainly indicate : 



(1.) The respiratory movements of Dragon-flies (Libellulae), and, 

 probably, of other insects also, are naturally subject to considerable 

 and frequent variations in force and rate, the causes of many of 

 these variations being as yet unknown. 



(2.) The respirations of these insects are always quickened by 

 exercise, emotion, rise of temperature, galvanism, and mechanical 

 irritation ; and the last three agents quicken them in the decapitated, 

 as well as in the perfect, insect. 



(3.) The respiratory movements of each segment of the trunk are, 

 in some measure, independent of those of the rest, although in the 

 perfect insect they concur in all the segments. They continue to 

 be performed, though feebly and slowly, in separated segments, pro- 

 vided their nervous cords and ganglia are entire : and they may be 

 abolished in single and successive segments by the local action of 

 chloroform. 



(4.) The removal of the head, including the supra- and sub-oeso- 

 phageal ganglia, does not, like the removal of the medulla oblongata 

 of the vertebrate animal, put a stop to the respiratory movements of 

 the insect ; but it diminishes their frequency and force, and deprives 

 them of all influence of the will and of mental emotions. 



(5.) The shock inflicted by the sudden destruction of the head, or 

 of the terminal part of the abdomen, generally stops all the respira- 

 tory movements of the insect for a time, and much enfeebles them 

 during the remainder of its life. 



(6.) The general tendency of the observations is to corroborate 

 the opinion of the self-sufficiency of the several ganglia for the 

 movements of their appropriate segments, and, thus far, to maintain 

 the belief in their essential independence. At the same time, the ob- 



s 2 



